N-isobutenyl-2-benzothiazole sulfenamide



Patented July 10, 1951 N -ISOBUTEN.YL2-BENZOTHIAZOLE SULFENAMIDE George E. P. Smith, Jr., Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application June 21, 1949, Serial No. 100,549

1 Claim. 1

This invention relates to a new class of chemical compounds which are valuable accelerators for the vulcanization of natural or synthetic vulcanizable rubbers. This application is a continuation-in-part of my copending application Serial No. 543,054, filed June 30, 1944, now abandoned.

.An object of the invention is to provide a new class of compounds useful as accelerators for the vulcanization of a rubber. Other objects Will be apparent .in the description of the invention which follows.

The objects of the invention are realized through the discovery of a new class of chemical compounds which are derivatives of sulfenamide (HSNHz). The compounds may be conveniently prepared by oxidizing a mixture of a Z-mercaptothiazole and a primary amine containing an alkenyl radical. The oxidation may be efiected by treating a mixture of the amine and the mercaptothiazole in an alkaline aqueous medium with an oxidizing agent, such as chlorine, bromine, iodine, hypochlorous acid, hypobromous acid, hypoiodous acid, or alkali metal or alkaline earth metal salts of said acids. The new class of products produced possesses the following formula:

wherein R1 and R2 are hydrogen or radicals derived from hydrocarbons or together represent a cyclic radical, and R3 is an alkenyl or cycloalkenyl radical.

Examples of amines which may be used in forming the accelerators include the following:

Allyl amine Crotonylamine Gamma methyl crotonyl amine Isobutenyl amine 2,3,4,5-tetrahydrobenzyl amine Alpha, beta-dimethylallyl amine Beta, gamma-cyclohexenyl amine Gamma, delta-butenyl amine Gamma, delta-cyclohexenyl amine Isopropenyl amine Alpha, beta-cyclohexenyl amine Isocrotonyl amine The Z-mercaptothiazole employed may be an aromatic thiazole, wherein R1 and R2 of the above formula represents an ortho-arylene radical. Examples of ortho-arylene radicals include benzo, 4-pheny1benzo, B-phenylbenzo, naphtho, .and

homologs or the various ring substitution products ofthese radicals; as typical ring substituents there may be mentioned nitro, halogen, hydroxy and alkoxy groups. R1 and R2 may together form a non-aromatic divalent radical, such as the various hydrogenated or partially hydrogenated benzo radicals; examples of mercaptothiazoles of this type are 2-mercapto-tetrahydro-benzothiazole and ring substitution products thereof. The mercaptothiazole may, however, be a member of the .so-called non-aromatic thiazoles, some examples being the following:

Z-mercaptothiazole 2-mercapto-4-methyl-thiazole Z-mercapto4,5-dimethyl-thiazole 2-mercapto-4-ethyl-thiaz01e 2-mercaptol-phenyl-thiazole 2-mercapto-l-phe,nyl-5-methyl-thiazole 2-mercapto-4-pr0py1-thiaz01e The following examples are given in further illustration of the invention. 7

Example 1 To 10.75 grams of commercial 2-mercaptobenzothiazogle there were added 5.5 grams of solid sodium hydroxide dissolved in about ml. of water. After reaction was complete the solution was filtered. The resulting clear solution of the mercaptothiazole was mixed with 42.5 grams of primary isobutenyl amine, and the mixture was diluted witha-bout 300 ml. of water. The alkaline mixture was then treated with a solution of 15.2 grams of iodine and 20 grams of potassium iodide in water, by adding the oxidizing iodine solution dropwise to the agitated ,ala-kline mixture. ,A white solid precipitated during the addition of the iodine. After the addition of all the iodine, the precipitate was collected, washed with water and dried, resulting .in 9.5 :grams of product. The latter was purified by recrystallization from petroleum ether. The purified substance melted at 64-66 and is N-isobutenyl-Z-benzothiazole sulfenamide, having the formula accelerators mercaptobenzothiazole and 2,2-dithiobis-benzothiazole, the latter being a delayed action accelerator, in the following rubber formula:

Ingredients: Parts by weight Rubber (smoked sheets) 100.00 Sulfur 3.00 Zinc oxide 5.00 Stearic acid 1.10 Accelerator 0.75

Samples of the three rubber compositions, so formulated, were heated for 60 minutes at 240 F. to determine whether or not they possessed any termine the relative accelerating properties of the respective accelerators and the following data were obtained:

Modulus of Elia gtifity s'lgensile1 in s. in. rengt Accelemm at elongain lbs/in? tion of at break 600% Mercaptobenzothiazole 650 2, 700 2,2'-DithiObis-benzothiazole 750 3, 150 N-Isbutenyl-2-benzothiazole sulfenamide. 2, 000 3, 675

The two sets of testing data given above show that the sulfenamide derivative from isobutenylamine and mercaptobenzothiazole is an excellent delayed-action accelerator, since the rubber composition including it did not vulcanize at the relatively low temperature of 240 F., in contrast with the composition including the standard accelerator, mercaptobenzothiazole. Furthermore, the new accelerator imparted very high physical properties to the rubber composition after a short cure at 280 F., in comparison with mercaptobenzothiazole and the standard delayed-action accelerator, 2,2'-dithiobis-benzothiazole.

Example 2 To 57.09 grams (1.00 mole) of allylamine there was added slowly and with stirring, at a temperature of l0 0., 210 ml. of 2.91 molar sodium hypochlorite solution (0.625 mole). As soon as the addition of the hypochlorite solution was complete, 350 ml. of an aqueous solution of 0.5 mole of the sodium salt of 2-mercaptobenzothiazole was added to the cold reaction mixture. The solid reaction product precipitated and was separated by filtration. After several recrystallizations from gasoline the product melted sharply at 61-62 C. The product, N-allyl-2-benzothiazole sulfenamide, has the following structure:

In accordance with either the method of Example or the method of Example 2, crotonyl amine may be reacted with Z-mercaptobenzothiazole to produce N-crotonyl-2-benzothiazole sulfenamide of the following formula:

These two additional sulfenamides are excellent delayed-action accelerators, having similar properties to N-isobutenyl-2-benzothiazole sulfenamide. Other sulfenamides of the invention may be prepared in analogous manners by oxidizing the mercaptothiazole with the appropriate primary amine, or by reacting the disulfide of the mercaptothiazole with the amine. Thus, for example, the following active delayed-action accelerators may be so produced:

N tetrahydrobenzyl-2-thiazole sulfenamide N-isobutenyl-Z tetrahydrobenzothiazole sulfenamide The invention is not limited to derivatives prepared in accordance with any particular method, but includes the preferred class of chemical compounds, however they may have been manufactured.

What is claimed is: N-isobutenyl-2-benzothiazole sulfenamide.

GEORGE E. P. SMITH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,268,467 Ashworth Dec. 30, 1941 2,382,793 Howland -2- Aug. 14, 1945 2,417,989 Moore Mar. 25, 1947 

